Production of positive colour images utilizing a photographic material containing a spiropyran compound and a polyhalogen compound

ABSTRACT

IN WHICH: X represents a methine group or nitrogen, Y represents hydrogen, a lower alkyl group or -CBr3, and Z represents the necessary atoms to close a benzene nucleus.   A photosensitive recording material containing a photosensitive dye-forming composition comprising: 1. AS DYE PRECURSOR COMPOUND AT LEAST ONE SPIROPYRAN COMPOUND, AND 2. AT LEAST ONE ULTRA-VIOLET SENSITIVE POLYHALOGEN COMPOUND CORRESPONDING TO THE FOLLOWING GENERAL FORMULA:

United States Patent [1 1 Van den Houte Dec. 16, 1975 1 PRODUCTION OF POSITIVE COLOUR IMAGES UTILIZING A PHOTOGRAPIIIC MATERIAL CONTAINING A SPIROPYRAN COMPOUND AND A POLYHALOGEN COMPOUND [75] Inventor: Jozef Willy Van den Houte,

Berchem, Belgium [73] Assignee: Agfa-Gevaert, Mortsel, Belgium [22] Filed: Sept. 26, 1974 [21] Appl. No.: 509,338

Related US. Application Data [62] Division of Ser. No. 334,247, Feb. 21, 1973,

abandoned.

[30] Foreign Application Priority Data 3,697,276 10/1972 Lewis et a1 96/48 R 3,708,297 1/1973 Poot et a] 961/90 R 3,847,611 11/1974 Royen et a1 96/48 R FOREIGN PATENTS OR APPLICATIONS 1,274,655 8/1968 Germany 96/90 PC 957,192 5/1964 United Kingdom 96/90 R Primary Examirier-Won H. Louie, Jr. Attorney, Agent, or FirmWilliam J. Daniel ABSTRACT A photosensitive recording material containing a photosensitive dye-forming composition comprising:

1. as dye precursor compound at least one spiropyran compound, and

2. at least one ultra-violet sensitive polyhalogen compound corresponding to the following general formula:

X represents a methine group or nitrogen,

Y represents hydrogen, a lower alkyl group or CBr and Z represents the necessary atoms to close a benzene nucleus.

10 Claims, No Drawings CONTAINING A SPIROPYRAN COMPOUND AND A I POLYI-IALOGEN COMPOUND This is a division of Ser. No. 334,247, filed Feb. 21,

This invention relates to the production of positive colour images with recording materials containing a mixture of a photosensitive polyhalogen compound and a dye precursor compound and to recording materials containing such mixture.

. Non-silver free-radical photography by means of recording materials containing a mixture of a photosensitive polyhalogen compound such ,as carbon tetrabro mide and a dye precursor compound such as leuco crystal violet has been described already in the United Kingdom Patent Specification 1,180,883.

These recording materials are suited for the production of print-out colour images i.e., colour images having reverscd image values with respect to the original.

1t is an object of the present invention to provide non-silver photographic colour-forming materials that offer the possibility of producing positive dye images starting from a positive original.

It is another object of the present invention to provide a photographic colour-forming process of the freeradical type resulting in the production of positive colour images.

Other objects and advantages of the present invention will appear from the following description.

According to the present invention a photosensitive material is provided containing a photosensitive dyeforming composition comprising:

1. as dye precursor compound at least one spiropyran compound, and 2. at least one ultraviolet-sensitive polyhalogen compound corresponding to the following general formula:

in which: X represents a methine group or nitrogen, Y represents hydrogen, lower alkyl, e.g., methyl, or

CBr and Z represents the necessary atoms to close a benzene nucleus including a substituted benzene nucleus e.g.,

a benzene nucleus substituted with groups such as methyl, methoxy, and halogen.

A preferred polyhalogen compound is Z-tribromomethylquinoxaline (ref. J. Chem. Soc. 1928, 1974). The bromination of the corresponding 2-methyl quinoxaline is carried out preferably according to the following procedure:

A mixture of 330 g of sodium acetate, 660 g of acetic acid and 0.64 mole of Z-methylquinoxaline is heated till the temperature reaches 70C. With thorough stirring at this temperature 315 g (1.9 mole) of bromine dissolved in 600 ml of acetic acid are added within 75 min. Thereupon the reaction mixture is boiled for 5 h, subsequently cooled down and finally poured into water. The precipitate formed is filtered by suction. washed with water, and recrystallized from ethanol. Melting point of the 2-tribromomethyl-quinoxalinc formed: 1 12C.

Preferred dye precursor compounds for use according to the present invention are spiropyran compounds containing at least one pyran ring having in the orthoand, metaposition with respect to the oxygen atom a condensed benzo or naphtho ring or other aromatic polycyclic ring system including these condensed rings or ring systems in substituted state e.g., an anthraceno or a phenanthreno ring system e.g., as present in a spirodibenzopyran, a spirodinaphthopyran, a spirobenzonaphthopyran, a 1,3,3-trimethylindolinobenzospiropyran. a 1,3,3trimethylindolinonaphthospiropyran or such spiropyrans containing condensed aromatic nuclei of the anthracene or phenanthrene type.

ln said spiropyrans the pyran rings, the condensed benzo. the condensed higher aromatic rings as well as the 1,3,3trimethylindolino ring may be substituted.

Suitable substituents therefore are e.g., hydrocarbon groups such as alkyl groups, e.g., lower alkyl groups such as methyl, substituted alkyl groups e.g., halogensubstituted alkyl groups or p henyl-substituted alkyl groups, alkylene ester groups e.g., a -CH -COOC H group, alkylene carboxyl groups e.g. a -CH COOH group, alkylene carbonamide groups or such groups substituted in the carbonamide group e.g., a

-CH -CONH- group, an acyl group e.g., acetyl, halogen, nitro, hydroxy, an alkoxy or aryloxy group or a substituent linking the carbon atoms in 3,3-position in the spiropyran system together e.g., a (CH ),,-chain wherein n is 2 or General formulae covering particularly suited spiropyrans are the following:

-CH2-CONH-@ halogen, nitro, hydroxy, an alkoxy or aryloxy group. a phenyl group or a substituted phenyl group or piperidyl, or R and R together represent a -(CH chain wherein n 2, or 3 to link the carbon atoms in the 3- and 3'-positions together.

Suited spiropyran compounds and their preparation are described in the published German Patent Applications 1.274,655 filed December 15, 1965 by Telefunken Patentverwertungs G.m.b.1-l., 1,269,665 1,286,110 1,286,111 and 1,286,112 all filed Sept. 30, 1966 by Telefunken Patentverwertungs G.m.b.H., and by W. Dilthey, Berres, Holterkoff, Wubken, JPmkLC/r. [2] 114, 187 (1926), by C. F. Koelsch and W. R. Workman in J.A.C.S. 74, 6288 (1952) and by l. M. Heilbron and G. F. Howard in J.Chem.S0c.(1934), 1571.

Preferred spiropyran compounds are spirodinaphthopyrans and spirobenzonaphthopyrans including such compounds wherein the naphthoand/or benzo ring(s) is (are) substituted.

An illustrative list of particularly useful spiropyran compounds is given in the following Table 1.

Table 1 Spiropyran compound Melting point CH -COOH CH -COOC H Table l-continucd Spirnpymn compound Melting point QcHa OCH 15. O o 0 O0 168 l8. 0 O 1 l0 OCH OCH Table l-continued Spiropyrun compound Br- CH OCH OCH

Melting point (C) Table l-continued Spiropyran compound Melting point (Ti In order to illustrate in more details the preparation of the spirobi(arylopyran)-compounds and the spiro- (indolino, arylopyran)-compounds the following preparation receipts are given:

PREPARATION 1 Preparation of 3-methyldi-,8-naphthospiropyran (compound 2 of Table 1) In a 2 litre three-necked flask, fitted with a reflux condenser and a gas inlet tube reaching nearly the bottom of the flask are introduced:

ethanol butanone 2-hydroxyl -naphthaldehyde l litre 22 ml (0.25 mole) 86 g (0.5 mole) The flask is shaken until partial dissolution of the ingredients. Dry hydrogen chloride gas is introduced at a rate, which allows complete absorption and the start of ethanol reflux. Thereupon the already highly blue coloured mixture is cooled down in a mixture of ice and sodium chloride and the introduction of hydrogen chloride gas is continued until saturation. In the reaction mixture green crystals of pyrylium salt form and the crystallization is allowed to proceed overnight in a refrigerator.

The pyrylium salt formed is separated by suction, washed with ethanol, and thereupon brought into suspension in 300 ml of ethanol.

A 10 by weight aqueous solution of ammonium hydroxide is added with stirring until the mixture is definitely alkaline. During this operation the mixture turns colourless.

The obtained crystalline product is separated by suction, washed with water, and dried.

Finally the spiropyran compound is recrystallized from 600 ml of benzene, again separated, and dried under reduced pressure at 5060C.

Yield: 45 g. Melting point: 204C.

PREPARATION 2 Preparation of l,3 ,3-trimethylindolinobenzopyrylospiran (compound 22 of Table I) In a 100 ml flask fitted with a reflux condenser the following ingredients are introduced:

salicylaldeh yde l,3.3-trimethyl-2-methylene-indolenine ethanol 3.7 g (0.03 mole) 5.] g (0.03 mole) ml The solutionis refluxed for 2 h, cooled, and filtered.

To the filtrate water is added for separation of a solid product. The solid is separated by suction, washed with water, and dried under vacuum conditions.

The spiran compound is recrystallized from 15 ml of hexane.

Yield: 5 g. Melting point: 93-94C.

It is assumed that during the photoexposure a dye stuff salt having the pyrylium structure forms when a spirobi(arylopyran) compound is used and that a dyestuff salt having the indolinium salt structure forms when a spiro(indolino-arylopyran) compound is used.

The recording material of the present invention preferably contains the photosensitive compound and dye precursor compound in a binder layer or sheet in which the binder has a hydrophobic character.

Particularly suitable binding agents for use in record ing layers of the present invention are hydrophobic polymers and copolymers e.g., containing styrene, vinyl acetate, acrylonitrile, acrylic acid ester, methacrylic acid ester or butadiene units, hydrophobic cellulose derivatives, phenoxy resins or polycondensates of the polyester type e.g., polycarbonates.

The recording layers of the present invention can obtain an improved ultra-violet and/or lightsensitivity by incorporating therein the sensitizing agents described in the United Kingdom Patent Application No. 41 ,749/70 corresponding with published Dutch Patent Application 71/ 12021.

Particularly useful sensitizing agents are organic compounds containing a carbonyl group linked through a conjugated system to a dialkylamino group e.g., Michlers ketone and l-methyl-3-phenyl-7-dimethylamino-2( l H )-quinolone. Poly-N-vinylcarbazole and copolymers containing N-vinylcarbazole units are likewise good sensitizing agents but give rise to some background colouration. The N-vinylcarbazole polymer or copolymer may be used as binding agent so that no other binding agents are needed.

A particularly good sensitivity to visible light is obtained with merocyanine dyes, the following dye being an example thereof:

A very useful sensitizing agent for print-out colour image formation is 2-mercapto-benzothiazole. However, when used without fog-inhibiting compound the mercapto compound provides positive colour images with stained background.

Suitable fog-inhibiting compounds such as triphenylstibine are described in the published Dutch Patent Application 71/12021.

The recording layers of the present invention preferably contain the photosensitive polyhalogen compound and spiropyran compound in a molar ratio range of 1:2 to 50:1.

The amount of spiropyran compound in the recording layer is preferably at least 0.05 g per sq.m.

The recording composition of the present invention can be coated on any kind of support on which colour images have to he produced. Preferred supports are 14 paper and resin sheets e.g., those known from silver halide photography. The thickness of the recording layer may vary within relatively broad limits. Dry coatings preferably have a thickness of 3 to 20 microns.

In order to produce a positive colour image according to the present invention the recording material in a first step is image-wise exposed to active electromagnetic radiation (ultra-violet radiation and/or visible light). Visible light is only effective when a spectral sensitizing agent is used in combination with the photosensitive polyhalogen compound.

According to a first embodiment the image-wise exposure is of such a degree that a visible print-out image is formed directly.

According to a second embodiment the image-wise exposure is carried out in such a way that first a latent image is produced, which is converted into a visible dye image by means of a so-called optical development.

The optical development proceeds by non-differentially (overall) exposure of the recording layer containing the latent or barely visible image to visible radiation, whose wavelength(s) lie(s) in the spectral absorption band of the products formed by the image-wise exposure and image-wise interaction of the photoexposed ingredients (1) and (2) of the photosensitive composition. In the overall exposure no exposure light is applied, to which the photosensitive polyhalogen compound is inherently sensitive since as a result the effect of the image-wise exposure is masked by an overall colouration. It is therefore advantageous to use in the optical development exposure a cut-off filter absorbing all the light corresponding with the wavelength range that is inherently absorbed by the ingredients of the recording layer that has not been exposed previously.

In the step following the formation of the visible dye image the recording material is heated preferably in the range of to C. This heating is maintained till the initially formed colour image has been bleached and has disappeared.

Subsequently, an overall exposure with active electromagnetic radiation i.e. ultra-violet radiation and/or visible light preferably combined with infra-red radiation produces a colouration in the areas of the recording material that had not been image-wise exposed previously. The positive colour image obtained is stable at room temperature.

The following examples further illustrate the present invention. The percentages are: by weight unless otherwise indicated.

EXAMPLE 1 A photosensitive recording material was prepared by coating 5 g of Z-tribromomethylquinoxaline, 250 mg of di-B-naphthospiropyran, and 50 mg of Michlers ketone dissolved in 100 ml of a 5 polystyrene solution in a mixture of methylene chloride and 1,1,2-trichloroethane (3:1 by volume) on an unsubbed polyethylene terephthalate support.

The dried coating had a thickness of 5 microns.

The coating was image-wise exposed in contact for 20 sec. through a silver image transparency carrying graphic information. The image-wise exposure was effected with ultra-violet radiation in an ultra-violet copying apparatus known as ACT INA SH, a diazo-type copying apparatus of La Cellophane, Paris, France. A negative cyan colour image was obtained.

The negative colour image was bleached by heating the recording material between l20170C, a treating 15 time of l min. or less (eg. only 10 sec.) being necessary according to the temperature.

The thermally treated material was then overall exposed for 10 to 20 sec. to ultraviolet radiation in the same ACTlNA SH diazotype-copying apparatus.

A positive cyan image stable at room temperature was obtained.

EXAMPLE 2 r A photosensitive material was prepared as described in Example 1. The photosensitive coating was imagewise exposed for 2 sec. through a silver image transparency carrying graphic information. The exposure was effected with a 80 W high pressure mercury vapour lamp type HPL of N. V. Philips Gloeilampenfabrieken Eindhoven, The Netherlands, placed at a distance of 10 cm. A latent image was obtained, which was optically developed to a cyan visible image by means of an overall exposure lasting 1 min. and being carried out with-a 250 W infrared lamp (of N. V. Philips Gloeilampenfabrieken) emitting also in the visible range of the spectrum. During the overall exposure a cut-off filter (Corning C.S. 3-67) was used absorbing all the light having a wavelength smaller than 540 nm.

The negative image obtained was then bleached by heating the recording material between 120l70C, a treating time of 1 min. or less (e.g., only 10 sec.) being necessary according to the temperature.

Thereupon the thermally treated material was overall exposed for 10 to 20 sec. to ultra-violet radiation in the already mentioned ACTINA SH diazo-copying apparatus.

A positive cyan image stable at room temperature was obtained.

When the overall ultra-violet exposure of the thermally treated recording material was replaced by an overall exposure to visible light combined with infrared radiation by using the above described infra-red lamp a positive image was obtained within 20 to 40 sec.

When in the Examples 1 and 2 the di-B-naphthospiropyran was replaced by a same amount of spiropyran compound according to one of the structural formulae 2, 5, 7, 9, 10, 33, or 39 ofTable l, analogous results were obtained.

EXAMPLE 3 A photosensitive material was prepared by coating 0.5 g of 2-tribromomethylquinoxaline, 20 mg of the spiropyran compound No. 9 of Table l, 5 mg of Michlers ketone and ml of a 5 polystyrene solution in methylene chloride on an unsubbed polyethylene terephthalate support. The solution was applied at a wet coating thickness of 0.12 mm.

The dried coating was image-wise exposed in contact for 2 min. through a silver image transparency carrying graphic information. The image-wise exposure was effected with a CHEMCUT PHOTOPRINTER MODEL D-7 (Double Sided Photoprinter containing 9 ultra-violet fluorescent lamps of W each, covering an exposure area of 3600 cm2). A negative orange-red image was obtained.

This negative image was removed completely by heating the recording material for 5 sec. at 160C. A subsequent overall exposure with a 250 W infra-red lamp (of N. V. Philips Gloeilampenfabrieken Eindhoven, The Netherlands) yielded a positive orange-red image.

EXAMPLE 4 A photosensitive material was prepared by coating 0.5 g of 2-tribromomethylquinoline (w,w,w-tribromoquinaldine), 0.05 g of the spiran compound No. l of Table 1, 0.005 g of Michlers ketone, and 8 ml of a 5 solution of polystyrene in methylene chloride on an unsubbed polyethylene terephthalate support. The solution was applied at a wet coating thickness of 0.12

The dried coating was image-wise exposed in contact for 20 sec. in an ACTINA SH diazo type copying apparatus through an original being a silver image transparency carrying graphic information.

A negative deep-blue colour image was obtained.

The negative colour image was bleached by heating the recording material for 30 sec. at 160C.

The thermally treated recording material was then overall exposed for 10 sec. to ultraviolet radiation in the same ACTINA SH diazotype-copying apparatus. A positive blue dye image was obtained.

EXAMPLE 5 A photosensitive material was prepared by coating the following composition:

0.5 g of 2-(tribromomethyl)-quinoxaline,

0.04 g of di-B-naphthospiropyran,

0.01 g of Z-mercapto-benzothiazole 0.02 g of triphenylstibine,

0.5 g of polystyrene,

10 ml of methylene chloride, at a wet coating thickness of 0.12 mm to a non-subbed polyethylene terephthalate support.

The coated layer was dried at room temperature.

The dried coating was image-wise exposed in contact as described in Example 4. An intense blue print-out image was obtained.

The recording material was heated at C till only a faint yellow colour was left in the originally exposed areas.

The thermally treated recording material was then overall exposed for 10 sec. to ultraviolet radiation in the already mentioned ACTINA SH diazotype-copying apparatus. A positive blue dye image was obtained.

EXAMPLE 6 A photosensitive material was prepared by coating the following composition:

0.5 g of 2-(tribromomethyl)-quinoxaline 0.04 g of di-B-naphthospiropyran 0.5 g of poly-N-vinylcarbazole 0.02 g of triphenylstibine 10 ml of methylene chloride, at a wet coating thickness of 0.12 mm to a non-subbed polyethylene terephthalate support.

The coated layer was dried at room temperature.

The dried coating was image-wise exposed in contact for 10 sec. in an ACT [NA SH diazotype copying apparatus through an original being a silver image transparency carrying graphic information.

An intense blue print-out image was obtained.

The recording material was heated at 150C till only a faint yellow colour was left in the originally exposed areas.

The thermally treated recording material was then overall exposed for 10 sec. to ultra-violet radiation in the already mentioned ACTINA SH diazotype-copying apparatus. A positive blue dye image was obtained.

We claim:

1. A photographic process in which a positive color image is produced by the steps of:

l. imagewise exposing a photosensitive recording material containing a photosensitive dyeforming composition comprising:

a. as dye precursor compound at least one spiropyran compound of the group consisting of a spirodibenzopyran, a spirodinaphthopyran, a spirobenzonaphthopyran, a l,3,3-trimethylindolinobenzospiropyran, a l,3,3-trimethylindolinonaphthospiran or a spiropyran that contains an anthracene or phenanthrene nucleus,

b. at least one ultraviolet sensitive polyhalogen compound corresponding to the following general formula:

X represents a methine group or nitrogen, Y represents hydrogen, a lower alkyl group or -CBr and Z represents the necessary atoms to close a benzene nucleus, to ultraviolet radiation of an intensity sufficient to produce at least a colored image in the exposed areas, 2. heating the recording material until the colored image has been bleached, and 3. overall exposing the recording material to active electromagnetic radiation of an intensity sufficient to produce a color image in the initially unexposed areas thereof. I 2. A photographic process according to claim 1 wherein said spiropyran compound corresponds to one of the following general formulae:

wherein: R, R,, R,, R R R and R' each represent hydrogen, alkyl, alkyl substituted with halogen, alkyl substituted with an ester group, alkyl substituted with a carboxyl group, alkyl substituted with a N-phenylcarbamyl group, a hydroxy group, an alkoxy group, an aryloxy group, a phenyl group, piperidyl, acetyl, halogen, nitro, or R and R, together represent a CH ),,-chain wherein n 2 or 3 to link the carbon atoms in the 3 and 3' positions together.

3. A photographic'process in which a positive color image is produced by the steps of:

l. imagewise exposing a photosensitive recording material containing a photosensitive dye-forming composition comprising;

a. as dye precursor compound at least one spiropyran compound of the group consisting of a spirodibenzopyran, a spirodinaphthopyran, a spirobenzonaphthopyran, a 1,3,3-trimethylindolinobenzospiropyran, a 1,3,3-trimethylindolinonaphthospyran or a spiropyran that contains an anthracene or phenanthrene nucleus,

b. at least one ultraviolet sensitive polyhalogen compound corresponding to the following general formula:

image by uniformly exposing the recording material to light having a wavelength to which the initially exposed latent image portions are more sensitive than the initially non-exposed portions,

3. heating the recording material until the visible image has been bleached, and

4. overall exposing the recording material to active electromagnetic radiation of an intensity sufficient to produce a color image in the initially unexposed areas thereof. 4. A photographic process according to claim 3 wherein said spiropyran compound corresponds to one of the following general formulae:

wherein:

R, R, R,, R R R and R;, each represent hydrogen, alkyl, alkyl substituted with halogen, alkyl substituted with an ester group, alkyl substituted with a carboxyl group, alkyl substituted with a N-phenylcarbamyl group, a hydroxy group, an alkoxy group, an aryloxy group, a phenyl group, piperidyl, acetyl, halogen, nitro, or R and R together represent a CH chain wherein n 2 or 3 to link the carbon atoms in the 3 and 3' positions together.

5. A photographic process according to claim 1, wherein the overall exposure in step (3) is effected with ultra-violet radiation.

6. A photographic process according to claim 3, wherein the overall exposure in step (4) is effected with ultra-violet radiation.

7. A photographic process according to claim 1,

wherein the overall exposure in step (3) is effected with a combination of visible light and infra-red radiation.

8. A photographic process according to claim 3, wherein the overall exposure in step (4) is effected with a combination of visible light and infra-red radiation.

9. A photographic process according to claim 1, wherein the recording material in step (2) is heated to a temperature in the range of to C.

10. A photographic process according to claim 3, wherein the recording material in step (3) is heated to a temperature in the range of 100 to 180C. 

1. A PHOTOGRAPHIC PROCESS IN WHICH A POSITIVE COLOR MATERIAL IS PRODUCED BY THE STEPS OF:
 1. IMAGEWISE EXPOSING A PHOTOSENSITIVE RECORDING MATERIAL CONTAINING A PHOTOSENSITIVE DYE-FORMING COMPOSITION COMPRISING: A. AS DYE PRECURSOR COMPOUND AT LEAST ONE SPIROPYRAN COMPOUND OF THE GROUP CONSISTING OF A SPIROBENZONAPHTHOPYRAN, A SPIRODINAPHTHOPYRAN, A SPIROBENZONAPHTHOPYRAN, A 1,3,3-TRIMETHYLINDOLINOBENZOSPIROPYRAN, A 1,3,3TRIMETHYLINDOLINONAPHTHOSPRIAN OR A SPIROPYRAN THAT CONTAINS AN ANTHRACENE OR PHANANTHRENE NULCEUS, B. AT LEAST ONE ULTRAVIOLET SENSITIVE POLYHALOGEN COMPOUND CORRESPONDING TO THE FOLLOWING GENERAL FORMULA:
 2. HEATING THE RECORDING MATERIAL UNTIL THE COLORED IMAGE HAS BEEN BLEACHED, AND
 2. heating the recording material until the colored image has been bleached, and
 2. A photographic process according to claim 1 wherein said spiropyran compound corresponds to one of the following general formulae:
 2. optically developing said latent image to a visible image by uniformly exposing the recording material to light having a wavelength to which the initially exposed latent image portions are more sensitive than the initially non-exposed portions,
 3. A photographic process in which a positive color image is produced by the steps of:
 3. heating the recording material until the visible image has been bleached, and
 3. overall exposing the recording material to active electromagnetic radiation of an intensity sufficient to produce a color image in the initially unexposed areas thereof.
 3. OVERALL EXPOSING THE RECORDING MATERIAL TO ACTIVE ELECTROMAGNETIC RADIATION OF AN INTENSITY SUFFICIENT TO PRODUCE A COLOR IMAGE IN THE INITIALLY UNEXPOSED AREAS THEREOF.
 4. A photographic process according to claim 3 wherein said spiropyran compound corresponds to one of the following general formulae:
 4. overall exposing the recording material to active electromagnetic radiation of an intensity sufficient to produce a color image in the initially unexposed areas thereof.
 5. A photographic process according to claim 1, wherein the overall exposure in step (3) is effected with ultra-violet radiation.
 6. A photographic process according to claim 3, wherein the overall exposure in step (4) is effected with ultra-violet radiation.
 7. A photographic process according to claim 1, wherein the overall exposure in step (3) is effected with a combination of visible light and infra-red radiation.
 8. A photographic process according to claim 3, wherein the overall exposure in step (4) is effected with a combination of visible light and infra-red radiation.
 9. A photographic process according to claim 1, wherein the recording material in step (2) is heated to a temperature in the range of 100* to 180*C.
 10. A photographic process according to claim 3, wherein the recording material in step (3) is heated to a temperature in the range of 100* to 180*C. 